The universe is a vast tapestry of structures, from solar systems to superclusters. Galaxies, like our Milky Way, contain billions of stars and are grouped into clusters. The largest known structures are superclusters, linked by filaments and separated by voids.

Studying the early universe involves observing redshifts and cosmic microwave background radiation. Dark matter and dark energy play crucial roles in the universe's composition and evolution. Understanding these components helps unravel the mysteries of cosmic history and structure.

Structure and Components of the Universe

Describe the structure of the universe, from solar systems to superclusters of galaxies

• Solar systems consist of a star (Sun) or multiple stars and orbiting planets (Earth, Mars), moons (Luna, Titan), asteroids, and comets
• Galaxies are massive gravitationally bound systems containing billions of stars, gas, dust, and dark matter
  • Types of galaxies include spiral (Milky Way), elliptical (M87), and irregular (Large Magellanic Cloud)
  • Milky Way is our home galaxy, a barred spiral galaxy containing an estimated 100-400 billion stars
• Galaxy groups are small aggregations of galaxies, typically containing fewer than 50 galaxies (Local Group)
• Galaxy clusters are larger structures containing hundreds to thousands of galaxies (Virgo Cluster, Coma Cluster)
• Superclusters are the largest known structures in the universe, composed of multiple galaxy groups and clusters
  • Linked by filaments and separated by large voids
  • Laniakea Supercluster contains our Local Group and an estimated 100,000 galaxies
• Large-scale structure refers to the cosmic web of galaxies, clusters, and filaments that form the universe's overall structure

Key astronomical objects

• Quasars are extremely bright and distant active galactic nuclei powered by supermassive black holes
  • Among the most luminous objects in the universe, outshining entire galaxies
  • Useful for studying the early universe due to their high redshifts (up to z=7.5)
• Andromeda galaxy (Messier 31 or M31) is the closest large galaxy to the Milky Way, approximately 2.5 million light-years away
  • Largest galaxy in the Local Group with an estimated trillion stars
  • Similar in size and structure to the Milky Way, likely to collide with our galaxy in about 4.5 billion years

Studying the Early Universe

Early universe observations

• Redshift and the expanding universe provide evidence for the Big Bang theory
  1. Light from distant galaxies is redshifted due to the expansion of the universe
  2. The greater the redshift, the more distant the galaxy and the earlier in the universe's history we are observing
  3. Hubble's Law relates a galaxy's distance to its redshift: $v = H_0 \times d$, where $v$ is the recessional velocity, $H_0$ is the Hubble constant, and $d$ is the distance
• Cosmic microwave background (CMB) radiation is leftover radiation from the early stages of the universe, about 380,000 years after the Big Bang
  • Provides information about the universe's initial conditions and evolution
  • Observed as a nearly uniform background of microwave radiation with a temperature of about 2.7 K
• Primordial nucleosynthesis is the formation of light elements (hydrogen, helium, lithium) in the early universe, within the first few minutes after the Big Bang
  • Relative abundances of these elements provide evidence for the Big Bang theory and help constrain models of the early universe
  • Approximately 75% hydrogen, 25% helium, and trace amounts of lithium were formed

The Universe's Composition and Evolution

Dark matter and dark energy

• Dark matter is an invisible form of matter that interacts gravitationally but does not emit, absorb, or reflect light
  • Makes up approximately 27% of the universe's mass-energy content
  • Its presence is inferred from gravitational effects on visible matter
• Dark energy is a mysterious force causing the accelerated expansion of the universe
  • Comprises about 68% of the universe's total energy density
  • Its nature remains one of the biggest unsolved problems in cosmology
• Cosmic inflation is a theory proposing that the early universe underwent a period of rapid exponential expansion
  • Helps explain the uniformity of the CMB and the flatness of space
• Galaxy evolution describes how galaxies form and change over cosmic time
  • Influenced by factors such as mergers, star formation, and interactions with the intergalactic medium